The present invention relates to a mechanism for cutting fibers that are to be used as a reinforcing material in a molding compound. More specifically, the present invention relates to a rotary cutter for adjustably cutting fibers entrained within a flowing resin material.
U.S. patent application Ser. Nos. 09/491,925 and 09/766,355, incorporated by reference above, disclose a device and method for producing a fiber-reinforced resin molding compound that may be introduced directly to a molding device or machine. In the compounding process set forth in the aforementioned patent applications, a strand or strands of a reinforcing fiber, preferably a glass fiber, is entrained within a flow of molten resin in a predetermined weight percent or volume ratio. The fibers are cut into predetermined lengths after having been entrained within the flowing, molten resin. Two devices or methods for cutting the reinforcing fibers are disclosed in the aforementioned patents.
A first method for cutting the reinforcing fibers takes advantage of the cutting action of an extruder auger flight against the bore within which it is housed. In this method, the entrained reinforcing fiber is directed into an injector or feed extruder. As the entrained reinforcing fibers are fed into the injector or extruder, the tight working fit between the auger flights and their housing acts to cut the reinforcing fibers. While simple and relatively wear resistant, this method does not provide a reliable means for cutting the fibers to repeatable lengths.
Another mechanism comprising a reciprocating blade is also disclosed in the aforementioned patents. This mechanism comprises a housing having a bore formed therethrough for the passage of the fiber/resin compound and a blade that is positioned across the bore of the housing bore. The blade has at least one aperture formed therethrough. As the blade is caused to reciprocate, the aperture formed through the blade is periodically brought into alignment with the bore formed through the housing. When the aperture is aligned with the housing bore, the fiber/resin mixture may pass therethrough. But, because the blade is reciprocating in such a manner as to withdraw the aperture out of alignment with the bore formed through the housing, the relatively sharp edge of the aperture will cut the reinforcing strands entrained within the flowing, molten resin as the edge of the aperture is withdrawn past the wall of the housing bore. The length into which the strands of reinforcing fiber are cut is controlled by altering the frequency at which the blade reciprocates. Again, this device is relatively simple, however, any wear to the blade will rapidly degrade the cutting efficiency of the device. In addition, this type of cutting device produces an unnecessary resistance to the flow of the molten resins and entrained fibers during the period when the housing bore is covered by the blade.
Accordingly, there is a need for a cutting mechanism that has a minimal resistance to flow of molten resin and entrained fiber and that operates in a continuous manner.
Another object of the present invention is to provide a cutting mechanism that is adjustable to permit close control over the lengths into which the reinforcing fiber strands are to be cut.
Yet another object of the present invention is to provide a cutting mechanism whose performance will not be significantly degraded by normal wear. Coincidental with this object is the object of providing a cutting mechanism that is modular and easily maintained.
These and other objectives and advantages of the invention will appear more fully from the following description, made in conjunction with the accompanying drawings wherein like reference characters refer to the same or similar parts throughout the several views.
The objects of the invention are met in a cutting mechanism that is capable of cutting fibers that are already entrained in a viscous material such as a thermoplastic resin. The cutting mechanism essentially comprises a housing having a bore formed therein, a bed knife disposed within the bore in the housing, and a rotating cutter. The housing has an inlet and an outlet. Reinforcing fibers entrained within a viscous molding material enters the housing through its inlet and passes through the inlet channel of the bed knife, the bed knife being arranged within the bore of the housing such that the inlet channel of the bed knife is substantially aligned with the inlet of the housing. The rotating cutter has a plurality of gullets formed therethrough around its periphery. The gullets may take many different shapes but are located on the rotating cutter such that as the cutter rotates with respect to the bed knife, the gullets are rotated past the inlet channel formed through the bed knife. In this manner, the reinforcing fibers and the molding materials in which they are entrained pass into the gullets and are subsequently severed.
Preferably the rotating cutter will remain in substantially full facial contact with the bed knife, but in general, misalignments of up to three thousandths of an inch may occur without degrading the cutting efficiency of the cutting mechanism. In order to maintain the necessary alignment of the rotating cutter and bed knife, it is desirable to provide a biasing structure for biasing the rotating cutter into substantially full facial contact with the bed knife. The biasing structure comprises a biasing rod that is constructed and arranged to resiliently apply pressure to the rotary cutter in a direction that is substantially normal to the surface of the bed knife. The biasing mechanism may also comprises a mechanical stop that prevents the movement of the biasing rod away from the bed knife. In this manner the movement of the rotary cutter away from the bed knife may be limited to no more than three thousandths of an inch as indicated.
The gullets of the rotating cutter of the cutting mechanism may comprise any number of shapes and arrangements. However, a preferred embodiment comprises a number of cylindrical bores formed through the rotating cutter. The bores have a leading edge and a trailing edge, the trailing edge being sufficiently sharp to sever a fiber protruding from the inlet passage of the bed knife into the gullet of the rotating cutter. The cylindrical bores may be formed normal to the planar cutting surface of the rotating cutter or may be inclined with respect to the cutting surface of the cutter. The gullets may also comprise a series of cutouts formed into the outer edge of the rotating cutter. The cutouts also have a leading edge and a trailing edge, with the trailing edge being formed so as to sever a fiber protruding from the inlet passage of the bed knife into the gullet of the rotating cutter. As with the cylindrical bores, the cutouts may be formed normal to the planar cutting surface of the rotating cutter or may be inclined with respect to the cutting surface of the cutter.
The present invention may also be characterized as a system for preparing fiber reinforced molding materials. This system comprises a viscous entrainment compounding device for compounding a continuous strand of reinforcing fiber with a molding material in a predetermined ratio and a cutting mechanism that is constructed and arranged to cut the continuous strand of reinforcing fibers into predetermined lengths. The viscous entrainment compounding device is constructed and arranged to convey the compounded continuous strand of reinforcing fiber and molding material to the cutting mechanism which, after cutting the fiber, conveys the fiber reinforced molding material to an output device that may be one of many different devices, including an injection molding press, conveying device, or preform fabricator.
A preferred cutting mechanism comprises a housing having a bore with an inlet and an outlet formed therein, a bed knife disposed within the bore in the housing, and a rotating cutter. The bed knife has an inlet channel formed therethrough that is arranged within the bore of the housing such that the inlet channel of the bed knife is substantially aligned with the inlet of the housing. The rotating cutter has formed entirely therethrough a number of gullets. These gullets are located on the rotating cutter such that as the cutter rotates with respect to the bed knife, the gullets are rotated past the inlet channel formed through the bed knife in substantial alignment therewith. Preferably the viscous entrainment compounding device will convey the continuous strand of reinforcing fiber therethrough by means of viscous shear forces imparted to the reinforcing fiber by molding materials being conveyed through the viscous entrainment compounding device under pressure.
Yet another characterization of the present invention is as a cutting mechanism for cutting fibers entrained in a viscous material that comprises a housing having a cavity with an inlet and an outlet formed therein; a bed knife having an inlet substantially aligned with that of the housing and a substantially planar cutting surface arranged to face the interior of the cavity; and, a rotating cutter supported upon and rotated by a pilot shaft, the rotating cutter having a substantially planar cutting face that is in substantially full facial contact with the cutting surface of the bed knife, the rotating cutter further having a plurality of gullets formed therethrough in substantial alignment with the inlets of the housing and the bed knife so that the fibers entrained in the viscous material may be received therethrough, the gullets each having a trailing edge that is constructed and arranged to sever the fiber as the trailing edge of the gullet passes the inlet of the bed knife, the resulting mixture of cut fibers and viscous material passing from the cavity of the cutting mechanism through the outlet of the housing.
The cutting mechanism may also comprise a backflow auger that is also received over the pilot shaft. The backflow auger is disposed within the cavity of the housing and is spaced away from the rotating cutter to define therebetween an annular passage into which the mixture of cut fibers and viscous materials may flow. The mixture of cut fibers and viscous materials then exits the housing through its outlet, which is in fluidic communication with the annular chamber. The back flow auger has grooves formed in its sides that act in conjunction with the walls of the cavity to prevent substantially all of the mixture of cut fibers and viscous materials from exiting the annular passage except through the outlet of the cavity formed through the housing.
A sealing collar received over the pilot shaft between the backflow auger and the rotating cutter forms respective seals between the backflow auger and the sealing collar and between the sealing collar and the rotating cutter so as to prevent substantially all contact between the mixture of cut fibers and viscous materials and the pilot shaft.
A biasing mechanism for resiliently biasing the rotating cutter into substantially full facial contact with the bed knife is preferably also part of the present invention. The biasing mechanism typically comprises a biasing rod that is passed through a longitudinal bore formed completely through the pilot shaft. A distal end of the biasing rod contacts the rear surface of the rotating cutter so as to force the cutter into contact with the bed knife. The biasing forces exerted upon the biasing rod derive from a spring mechanism that may be coupled to a base end of the biasing rod. Where appropriate, a mechanical limiting mechanism may be coupled to the biasing rod so as to prevent the rotating cutter from moving more than approximately three-one thousandths of an inch away from the bed knife.
A drive mechanism is coupled to the housing of the cutting mechanism for the provision of motive power to the rotating cutter. The drive mechanism comprises a motor that is operatively coupled to a drive shaft by a transmission mechanism. The drive shaft is in turn coupled to the pilot shaft of the cutting mechanism for rotating the rotating cutter with respect to the bed knife. Due to the high heat required where the cutting mechanism is used in conjunction with thermoplastic resins, it is preferable to couple the drive mechanism of the present invention to the cutting mechanism in a thermally isolated manner.